Commit dcba7108 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/livepatching

Pull livepatching fix from Jiri Kosina:
 "Fix the way how livepatches are being stacked with respect to RCU,
  from Petr Mladek"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/livepatching:
  livepatch: Fix stacking of patches with respect to RCU
parents 021f6019 842c0884
......@@ -59,7 +59,11 @@ static void notrace klp_ftrace_handler(unsigned long ip,
ops = container_of(fops, struct klp_ops, fops);
rcu_read_lock();
/*
* A variant of synchronize_sched() is used to allow patching functions
* where RCU is not watching, see klp_synchronize_transition().
*/
preempt_disable_notrace();
func = list_first_or_null_rcu(&ops->func_stack, struct klp_func,
stack_node);
......@@ -115,7 +119,7 @@ static void notrace klp_ftrace_handler(unsigned long ip,
klp_arch_set_pc(regs, (unsigned long)func->new_func);
unlock:
rcu_read_unlock();
preempt_enable_notrace();
}
/*
......
......@@ -48,6 +48,28 @@ static void klp_transition_work_fn(struct work_struct *work)
}
static DECLARE_DELAYED_WORK(klp_transition_work, klp_transition_work_fn);
/*
* This function is just a stub to implement a hard force
* of synchronize_sched(). This requires synchronizing
* tasks even in userspace and idle.
*/
static void klp_sync(struct work_struct *work)
{
}
/*
* We allow to patch also functions where RCU is not watching,
* e.g. before user_exit(). We can not rely on the RCU infrastructure
* to do the synchronization. Instead hard force the sched synchronization.
*
* This approach allows to use RCU functions for manipulating func_stack
* safely.
*/
static void klp_synchronize_transition(void)
{
schedule_on_each_cpu(klp_sync);
}
/*
* The transition to the target patch state is complete. Clean up the data
* structures.
......@@ -73,7 +95,7 @@ static void klp_complete_transition(void)
* func->transition gets cleared, the handler may choose a
* removed function.
*/
synchronize_rcu();
klp_synchronize_transition();
}
if (klp_transition_patch->immediate)
......@@ -92,7 +114,7 @@ static void klp_complete_transition(void)
/* Prevent klp_ftrace_handler() from seeing KLP_UNDEFINED state */
if (klp_target_state == KLP_PATCHED)
synchronize_rcu();
klp_synchronize_transition();
read_lock(&tasklist_lock);
for_each_process_thread(g, task) {
......@@ -136,7 +158,11 @@ void klp_cancel_transition(void)
*/
void klp_update_patch_state(struct task_struct *task)
{
rcu_read_lock();
/*
* A variant of synchronize_sched() is used to allow patching functions
* where RCU is not watching, see klp_synchronize_transition().
*/
preempt_disable_notrace();
/*
* This test_and_clear_tsk_thread_flag() call also serves as a read
......@@ -153,7 +179,7 @@ void klp_update_patch_state(struct task_struct *task)
if (test_and_clear_tsk_thread_flag(task, TIF_PATCH_PENDING))
task->patch_state = READ_ONCE(klp_target_state);
rcu_read_unlock();
preempt_enable_notrace();
}
/*
......@@ -539,7 +565,7 @@ void klp_reverse_transition(void)
clear_tsk_thread_flag(idle_task(cpu), TIF_PATCH_PENDING);
/* Let any remaining calls to klp_update_patch_state() complete */
synchronize_rcu();
klp_synchronize_transition();
klp_start_transition();
}
......
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